1. Field of the Invention
The present invention relates to an image forming apparatus for use in image formation using an electrostatic photocopying process such as photocopiers, facsimile machines, printers, etc.
2. Discussion of the Background
Recently, high speed, size reduction and high definition full color images have been demanded for image forming apparatuses for use in image formation using an electrostatic photocopying process such as a photocopier or a printer. To obtain such high definition images, toners having a small particle diameter are used irrespective of the kind of the toners, i.e., pulverized toners and polymerized toners. However, such small-sized toners have a large surface area per a unit weight and therefore the toners have low fluidity and relatively large adhesion. This leads to deterioration of cleaning performance of removing residual toner particles. Therefore, an external additive functioning as a fluidizer is added in a large amount of quantity to the toner to compensate for the decrease in the fluidity. Nevertheless, there is still a disadvantage in that good cleaning performance for such a toner is not securely obtained.
In addition, spherical toners are typically used to obtain a high definition image because such toners have good developability and transferability. Spherical form toners have good fluidity but tend to roll. This leads to a problem in that, when a blade cleaning system is adopted in a high speed image forming apparatus, the toner particles sneak through the blades, resulting in poor cleaning performance.
Cleaning systems are broadly classified into blade cleaning systems and brush cleaning systems. Blade cleaning systems are preferably used in a small-sized image forming apparatus in terms of structure and cost. Therefore, a blade cleaning system with good cleaning performance is desired even when spherical toners having a small particle diameter are used.
Countermeasures against the poor cleaning performance problem with toners having a small particle diameter and a spherical form can be taken from the standpoints of the toner and process.
As for a countermeasure from the standpoint of the toner, unexamined published Japanese Patent Application No. (hereinafter referred to as JOP) 2003-131537 discloses an image forming apparatus containing a cleaning device having a rubber blade and a mechanism for transporting toner particles collected by the cleaning device to a developing device, wherein the toner for use in the image forming apparatus has a volume average particle diameter (d) of from 4 to 10 μm and has a flatness ratio (d/t) of the volume average particle diameter (d) to the thickness (t) of from 2 to 5.
As for a countermeasure against the poor cleaning performance problem from the standpoint of process, JOP 2002-221886 discloses an image forming method in which the following relationships are satisfied: 0.2≧Y100−Y0≧0.01 and 2.95≧Y100/Y0≧1.15 (the unit of Y100 and Y0 is N·m), wherein Y0 represents the average value of dynamic torque created between an organic image bearing member and a cleaning blade when a toner image is not formed on the organic image bearing member and Y100 represents the average value of dynamic torque when a 100% solid toner image is formed on the organic image bearing member.
However, countermeasures from the standpoint of either toner or process are not sufficient to avoid the cleaning problem with toners having a small particle diameter and a spherical form. Especially an image forming apparatus having good ability is desired even when toners having a small toner particle diameter is used to satisfy the demands to produce high definition images at a high speed.
Because of these reasons, a need exists for an image forming apparatus in which toner particles remaining on the surface of an image bearing member can be removed with a cleaning blade even when the toner has a small particle diameter.